I’m trying to follow all the threads of this thing. What EXACTLY has been the material harm done by these leaks? Revealing? Yes. Embarrassing? Yes. But how is our national security at risk, i.e. how is your life and my life at risk? Seems like a lot of state dept types acting in typical non-professional manner is all.
By revealing what is known in diplomatic circles, the depth of surveillance can be surmised. In some cases, this could lead to physical harm to those who provided the data. In all cases it allows the enemy to profile our security capabilities.
Note that this is true even for information which does not surprise us. For instance, in the case of North Korea supplying some number of rockets to Iran none of us is surprised in the least. However, if the number is precise and thought by the Iranians to be a "secret", then they will start looking for how we could have known. Furthermore, it may key them in to other information which they had previously presumed to be a secret which now they will presume to be compromised.
In almost any game, you are at a disadvantage if your cards are shown. It is hard enough playing "defense" against these bozos without someone exposing our playing hand.
It does affect national security because it dampens a free and candid exchange of views. Nothing which has been relesed is really surprising or even unexpected in the course of normal diplomatic affairs but how many diplomats, knowing what could happen, would be prepared to give their unvarnished views of local affairs overseas in future?
This most certainly does affect national security.